Method for replacing program in portable information terminal using utility program and new program received via communication unit and determining utility program appropriateness for replacement

1. A method of replacing a program stored in a portable information terminal, said portable information terminal comprising a communication unit for transmitting to and receiving data from an external device, a memory unit for temporarily storing a new program and a utility program operating to carry out the replacement of a prestored program with the new program and a program storage unit for storing the prestored program and for replacing the prestored program with the new program, said method comprising: (a) receiving the new program and the utility program from an external device via said communication unit, and storing the new program and the utility program in said memory unit; and (b) replacing the prestored program in said program storage unit with the new program, using the utility program; wherein (a) comprises: (a1) storing in said memory unit the new program and the utility program received from said external device via said communication unit; and (a2) determining whether the new program stored in said memory unit is a program for replacing the prestored program stored in said program storage unit and determining whether the utility program stored in said memory unit is appropriate for replacing the prestored program with the new program.

2. The method of replacing a program stored in a portable information terminal as claimed in claim 1, wherein step (a) further comprises: (a3) determining whether a power supply in said portable information terminal can supply a sufficient voltage and current to replace the prestored programed stored in said program storage unit; (a4) removing any programs, other than the new program and the utility program, which are temporarily stored in said memory unit to secure sufficient space to execute the utility program; and (a5) executing the utility program stored in said memory unit if it is determined said power supply can supply a sufficient voltage in said (a3).

3. The method of replacing a program stored in a portable information terminal as claimed in claim 1, wherein said (b) comprises of: (b1) checking a size and checksum of the new program and the utility program stored in said memory unit to determine whether the new program and the utility program were correctly transmitted from said external device and stored in said memory unit; (b2) placing said program storage unit into a deletion and writing mode if the new program was correctly stored in said memory unit; (b3) deleting the prestored program in said program storage unit; (b4) storing the new program in said program storage unit; (b5) placing said program storage unit into a reading mode when the storage of the new program in said program storage unit is completed; and (b6) initializing the new program stored in said program storage unit if the new program was correctly stored in said program storage unit.